Use of a calculator should be convenient and adaptable to a user's needs. Because a calculator may be used many times in a day, great improvements in convenience are achieved by reducing mental effort required to enter numeric values or evaluate values displayed as output. More particularly, because values input to a calculator come from the user's needs and values output from the calculator must be applied to the user's needs, a calculator having data entry and data output corresponding to the user's needs is desirable.
Most calculators receive as input and display as output decimal numeric values where a decimal point separates a whole integer portion and a partial integer portion. For example, a value represented as "1.7" includes a whole integer portion "1" and a partial integer portion "7", representing a ratio of the values seven and ten. There exists, however, a need to manipulate fractions on calculators. Accordingly, there exists a need for convenient entry and display of such fractions on calculators.
A conventional method of entering numeric values represented as fractions is indirect. Such method requires mathematic operations and some degree of mental effort by the user. For example, to enter the fraction "3 and 5/8" the user, through a series of calculator operations, divides the value five by the value eight and adds the value three. On reverse polish machines, the user enters the values three, five and eight and executes the functions divide and add. However, this method requires three stack registers and mental effort in performing the mathematic operations of division and addition. It is, therefore, desirable that a calculator receive fraction values directly without mathematic operations to save register use and to reduce mental effort which may distract the user.
In a conventional method of displaying fractions on calculators, a given level of decimal precision is first established. The calculator then provides a fraction display having a whole number, numerator, and denominator based on the established level of precision. However, the denominator selected by the calculator is not likely to be directly applicable to the user's needs because the user is normally familiar with fraction values expressed with certain denominators. The output display then requires interpretation or conversion by additional mathematic operations for the user to appreciate its significance.